In the field of communication networks, one of the purposes of a communication network is to deliver information to an endpoint of that network for onward transmission, for further processing by manual or automated means, or for display or storage. The information is transmitted as the content (or payload) of messages within the network. The messages are routed and delivered based on a numerical address that accompanies the information. This information is desired by content consumers, specifically the humans or automated processing and storage systems associated with the network endpoints. However, this content is typically invisible to the transport mechanism employed within the network and, therefore, is not considered when performing addressing, routing or delivery operations.
Methods currently exist that attempt to allow content consumers to discover data based on the actual content available in a network as opposed to a numeric network address, or other fixed form of resource locator, for example a URL. The most well known method used to locate data on the Internet is performing a search using a search engine. Typically, an Internet search engine operates by indexing web pages and returns search results to the consumer based on its index. The index is typically created by using bots (software tools used for digging through data) to crawl through the Internet and examine content and index the findings. There are several drawbacks to this methodology. First, it takes time for the bots to crawl through the Internet indexing web pages. Typically, the time required for such indexing operations is twenty-eight days. Because of the time delay, the resultant index typically contains a multitude of links to web pages that have significantly changed or disappeared altogether since the beginning of the indexing cycle. Secondly, not all web pages are indexed. Thus, pertinent information may exist without any way for a user to access it other than by knowing the exact resource locator of the server that stores the pertinent information.
Another method in existence today for matching content to content consumers is by using channels, which is also closely related to publish/subscribe methods. Under both these methods, content consumers subscribe to or dial up a particular source or channel that carries a predefined range of content. An example of this is the now defunct Pointcast™ network. There are several disadvantages associated with distributing content based on this method. First, the content consumer still has to know where the desired channel is located. Second, the content consumer receives all the content on that channel whether or not he or she is interested in it. Further, such many-to-many event notification technologies such as publish/subscribe are stateless for scalability and robustness. Thus, they require parties to persistently re-send messages. As a result, network nodes need to re-compute the routing algorithm on each message received regardless of whether or not it is a new message. Also nodes that do not remember the outcome of a routing decision for a given data packet must re-compute the algorithm on each packet received. This forces a trade-off among scalability (number of senders and receivers), semantic expressiveness of subscription and advertisement language, and notification persistency (message frequency). This trade-off has limited the commercial deployment of event notification technologies to a limited scope (local area networks, limited number of senders or receivers, limited flexibility to express interest).